Well ok, I see, so formations are meant to be used on open fields should you happen to be on an open field, and it happens sometimes that you are in campaigns, although very rarely.

About inefficient use of units, I think these simple formations are inefficient but lets not dig deeper into it now. So about getting surrounded, of course you should do your best to not get surrounded but speaking from my experience, it is indeed very much possible to make a sort of a "box" or "wedge" formation which if it is sufficiently big, you don't care much about getting surrounded as the goal is to push through the open field. Usually if you find yourself in these rare open field scenarios what you should do is push in a blob.

So I remember myself using something you could call a formation on a few occasions on open fields. But it certainly wasn't homogenous or it didn't have any fixed shape. I think the proper term is a blob xD But of course like I said it is much larger and more of a "wedge" shape. And I wouldn't really call it a formation. That is the only instance when I think it would be efficient and effective.

@Elder but we have asked for the disclosure of all the cheese and we treat it seriously. Everyone on this site can get banned, everyone.
@Elder ale prosiliśmy o wyjawianie wszystkich serów i traktujemy to poważnie. Każdy na tej stronie może zostać zbanowany, każdy.

Aye, Pushing in a "blob" is indeed a fine strategy when the goal is to kill the enemy leader, although you will probably end up with more casualties. I was playing EI-undead crossing the other day, and decided this was a good time to test that Anti-undead formation myself. Admittedly, there were 1-3 level 2-3 units in there, but that can always be the case in these formations. As you might know, that particular scenario puts you up against lvl 2 undead, which could easily kill a cavalryman. Against my formation however, they could do absolutely nothing. Here, there was no open field, and the formation still worked. I think it is fair to say that they work on more than just open fields, and the reason they work is that the damage is spread out among a bigger group of units. Another reason is that, if you use them right, you only fight 1-3 enemies at the time, at least when you play against the AI.

Bear also in mind that, even if the objectiv is to kill the enemy leader, there may be other important things to take care of across the map, such as defending Leaders or villages, so concentrating all your forces at one point may simply not be an option. I do however very much value your arguing against the use of these formations, and, to my shame, I must admit to not being able to win Undead Crossing because the anti-undead formation cant get to the leader before the turn limit of 18 turns runs out.

You could put the level 0s in between two level 1s/veterans, that way even if the level 0 dies no one can move into its spot due to the ZOC of the two surrounding units. Actually this "solid line mixed with fodder" is my standard Wesnoth formation

An unstoppable formation is the elvish shyde/sylph fleet of death- that's one or two shydes plus a lot of sylphs, and they can fly around the map slaughtering everything in their path!

I don't know if this counts as a formation but I like to use "assassination squads" such as shadow/nightgaunts or rangers/avengers in the forest to sneak around and kill off enemy leaders. (A good example is the elvish treasury scenario in Legend of Wesmere, where sneaking a few rangers through the woods lets you finish extremely fast).

p.s. For posting images, I found imgur to work really well - you don't need to register and the images stay up for a long time (in fact they claim they'll never delete them but I'm skeptical about that).